An international conference is proposed on "The Chemistry and Biology of a2-Macroglobulin". The rationale for such a meeting at the present time is: Rapid progress has been made in the past three years on the mechanism by which macroglobulin reacts with proteases. The inhibitor has been found to contain a new (cys-glu thiolester) chemical group, and proteolytic enzymes bind at this site via lysyl amino groups. An unexpected homology has also been observed between and certain proteins of the complement system which also contain this reactive thiolester center. There has been direct application of these new chemical results to the interaction of with cells. This work bears on the study of clearance of proteases and other proteins from the circulation, and on the general area of receptor-mediated endocytosis. Despite the significance of these results, there has been no recent conference, or even a published review to integrate and evaluate this new information. It is generally assumed that the major function of macroglobulin is in the control of proteolytic in the plasma and othe tissues. The protein has also been implicated in several disease states although no definitive correlations have been found, and, in general, there is not a clear picture of its precise physilogic role. It is to be expected that convening the chemical, biologic and development of a broader perspective on a2-macroglobulin in biology.